I'd say Star Wars (original series) is the best. It was an original story not adapted from anything else, it created the summer blockbuster culture, its influence was and it's still spread over all fantasy movies/sagas including LOTR movies, it revolutionized the industry with its amazing special effects of its time, etc, etc etc.
LOTR was huge (and it's my favorite over SW), but it had some clear advantages:
#1 Funding. George Lucas financed each SW movie, sure he had help from his friend Coppola and others but it was mainly his wallet taking the hit. LOTR movies in this modern age were concieved and planned to be guaranteed blockbusters
#2 Over 4 Decades of fandom and mass popularity. This is self-explanatory. The movie was going to sell well even if it was a sub-par production, but this also helped the production greatly since they had all this "Middle Earth Lore" at their disposal not to mention priceless colaborations from long-time lotr fans and artists like Alan Lee and John Howe, and counteless nerds LOTR experts ranging from critics to teachers and philosophers. Even some important actors like Christopher Lee had a deep understading of the material and shared valuable input with the filmmakers.
#3 Peter Jackson. Seriously, NOBODY (movie director) would invest 6-7 years of his life making a project with so many SACRIFICES, specially when that project are back-to-back-to-back movies you don't have complete control over like Lucas did with his movies.
